This invention relates to pneumatically actuated resistance weld heads and reflow solder heads. More particularly, the invention relates to weld and reflow solder heads having an automatic cutoff of pressurized gas in a pneumatic cylinder when a desired weld force between an electrode and workpiece is attained.
For convenience, hereinafter the terms "weld" and "welding" shall refer to both resistance welding and reflow soldering systems and operations.
Air-actuated weld heads typically include an air cylinder which controls the upward and downward motion of one or more electrodes used to weld or reflow solder a workpiece. Such weld heads are adjustable and may be adapted for welding different types of workpieces.
Typically, different welding applications require different welding parameters. These parameters include the duration and magnitude of electrical weld energy, and the weld force, which is the force exerted on the workpiece by the electrode.
Typically, in known air-actuated weld heads, a maximum air pressure in the air cylinder is set separately from the weld force, which is usually set by precompressing a spring in the weld head connected between the air cylinder and the electrode. One problem associated with this manner of setting up the weld head for a new welding application is that, if set incorrectly, the air cylinder may continue to exert pressure on the electrode after the desired weld force has been attained resulting in excessive weld force.
In most weld heads, a force firing switch is operatively connected to the spring for sensing when the desired weld force is reached; that is, when the force applied by the air cylinder overcomes the precompression spring force. When the force firing switch activates in response to a desired weld force, it signals a microcontroller in a welding power supply to supply electrical current to the electrode(s) to initiate welding. The air cylinder is preset by manually setting pressure regulators on the air cylinder to a maximum pressure at which the force firing switch just activates. This is usually determined by first presetting the spring to the desired weld force and then performing a "dry run" with the air cylinder set to a pressure judged to be slightly above the target maximum pressure in the air cylinder corresponding to the desired weld force. During the dry run, the operator must first observe actuation of the force firing switch, note the pressure in the air cylinder, and then set the air cylinder pressure regulator for precisely that pressure. This procedure must be repeated any time a welding application requires a different weld force.
Such manual operation invites human error. This may occur in the form of an inaccurate initial setting, or by the operator forgetting to reset the air pressure in the cylinder for a new welding application. Such inaccurate settings can result in either an excessive or inadequate weld force, resulting in damaged welds or insufficient pressure to activate the force firing switch.
Furthermore, pressure settings in the air cylinder valves may drift, requiring subsequent adjustments to maintain the desired weld force. Such valve drift may go unnoticed through several welding operations, increasing the potential for unsatisfactory welds. Also, such continual adjustment increases the potential for human error.